Cardiac arrhythmia, such as atrial fibrillation, occurs when regions of cardiac tissue abnormally conduct electric signals to adjacent tissue, thereby disrupting the normal cardiac cycle and causing asynchronous rhythm. Important sources of undesired signals are located in the tissue region along the pulmonary veins of the left atrium and in the superior pulmonary veins. In this condition, after unwanted signals are generated in the pulmonary veins or conducted through the pulmonary veins from other sources, they are conducted into the left atrium where they can initiate or continue arrhythmia.
Procedures for treating arrhythmia include surgically disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathway for such signals. More recently, it has been found that by mapping the electrical properties of the endocardium and the heart volume, and selectively ablating cardiac tissue by application of energy, it is sometimes possible to cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions. An example of such ablation procedures is termed pulmonary vein isolation, and involves the ablation of tissue in the area adjacent the junction of the pulmonary veins and the left atrium. The resulting lesion(s) may isolate irregular electrical signals originating in the area from spreading through the rest of the atrium and disrupting the patient's heart beat.
For these and other applications, conventional practice may involve a two-step procedure. First, a mapping catheter having one or more electrodes for sensing electrical activity is used to measure electrical activity at the treatment area to identify target regions for ablation. In turn, an ablation catheter may then be positioned adjacent the target regions to deliver sufficient energy to form the non-conducting lesions. Accordingly, it would be desirable to provide a catheter and a technique for mapping and ablating tissue without the need to employ multiple catheters. Likewise, it would be desirable it reduce or avoid the need to reposition a catheter while performing mapping and ablation procedures. As will be described in the following materials, this disclosure satisfies these and other needs.